title: Extensive nucleolus organizer region polymorphism in Gymnotus carapo (Gymnotoidei, Gymnotidae).
abstract: An investigation was conducted on six populations of Gymnotus carapo from the Upper Parana river system in Brazil. A wide variability of the NOR-bearing chromosomes was found involving paracentric inversions in the heterochromatic regions associated with NORs, resulting in 5 NOR chromosome phenotypes. The distribution of the distinct NOR phenotypes varied both inter- and intrapopulationally. Results obtained using an exact test revealed that the six populations are in Hardy-Weinberg equilibrium. Although NOR size polymorphism is quite a common occurrence in fish karyotypes, this is the first description of a balanced polymorphism involving 3 different NOR chromosomes in 5 combinations.
authors.affiliation: Departamento de Biologia, Universidade de São Paulo, Brazil.
authors.forename: F M
authors.initials: FM
authors.lastname: Fernandes-Matioli
authors.forename: L F
authors.initials: LF
authors.lastname: Almeida-Toledo
authors.forename: S A
authors.initials: SA
authors.lastname: Toledo-Filho
mesh_terms: D000818:Animals; D004555:Electric Fish / Q000235:genetics*; D005260:Female; D014644:Genetic Variation; D008297:Male; D009697:Nucleolus Organizer Region / Q000235:genetics*; D010641:Phenotype; D010802:Phylogeny; D011110:Polymorphism, Genetic